The alkylation of benzene with olefins produces a variety of alkylbenzene compounds that have various commercial uses. Examples include the alkylation of benzene with olefins having 8 to 16 carbons for the production intermediate compounds in the manufacture of detergents. The alkylbenzenes are sometimes referred to as phenylalkanes, and are produced as a commodity in large scale facilities worldwide with production rates of between 50,000 and 200,000 metric tonnes per year. The alkylation process comprises reacting benzene with an olefin in the presence of a catalyst at elevated temperatures. The catalysts can be homogeneous or heterogeneous catalysts such as hydrogen fluoride, aluminum chloride, silica alumina, or zeolitic catalysts.
The desired alkylated compounds are monoalkylated aromatic compounds. Monoalkylated aromatic compounds include linear alkylbenzenes (LAB), which are used to form linear alkylbenzene sulfonates (LABS), a common compound used in the manufacture of detergents. Two common reactions for production of monoalkylated aromatic compounds are alkylation of aromatic compounds such as benzene and transalkylation of polyalkylated aromatic compounds. One aspect of benzene alkylation has been the use of high benzene to olefin ratios for the production of alkylbenzene production. The energy cost to recover the excess benzene has driven process designs to reduce the amount of benzene supplied to the reaction zone. This reduction has resulted in an increase in the amount of dialkylbenzene and trialkylbenzene byproducts produced in alkylation.
The desire to convert these polyalkylated benzene to monoalkylated benzene has resulted in further developments related to the transalkylation process. The transalkylation process reacts the polyalkylated aromatic compound with benzene to form a monoalkylated product, and thereby to increase yields of monoalkylated benzene. Both the alkylation and transalkylation processes involve the use of benzene in a relatively high molar ratio with respect the olefin or polyalkylated aromatic compound. The transalkylation process for producing a monoalkylated benzene product can be further complicated by the presence of polyalkylated benzenes that have alkyl groups having fewer carbon numbers than desired.
Currently, monoalkylated benzenes are desired, and polyalkylated benzenes are less desired by-products that need to be removed or need to be recycled to try and produce more monoalkylated benzenes. One method of reducing the amount of polyalkylated benzenes is to increase the benzene to olefin ratio used during alkylation. Another method of reducing polyalkylated benzenes is to pass the polyalkylbenzenes through a transalkylation reactor. However, the industry is striving to reduce the benzene to olefin ratio, and the usual method is to use many small beds with decreasing ratios as the benzene and olefins pass through successive beds. The cost of producing a pure benzene stream is expensive, and the cost of separating and recycling benzene is energy intensive and therefore expensive.
Methods of improving the recovery and usage of benzene, which also optimize the processing of alkylated benzenes that have alkyl groups having fewer carbon numbers than desired, can result in substantial savings in energy and expense.